There are many kinds of tablets and capsules that resemble one another in the size, color tone and shape. To identify each preparation, a company name, a company mark, a product name, active ingredient contents and the like are often coded and directly imprinted on the preparation. For imprinting, engraving and printing are available. While engraving is employed for plain tablets free of coating, a subset of film-coated tablets and the like, printing is employed for many film-coated tablets, sugar-coated tablets, capsules and the like.
For tablets and capsules, polishing with wax (in this specification, it means “wax” in a narrow sense, namely, fatty acid ester of higher alcohol: examples: carnauba wax, bees wax and the like) is often applied for the purpose of increasing the commercial value by glossy appearance, protecting a preparation from highly humid environment, preventing staining with coloring agents, improving slip property to facilitate handling in later operations of printing, inspection, packing and the like, and the like (e.g., Porter and two others, Pan Coating of Tablets and Granules, edited by Herbert A. Lieberman and one other, Pharmaceutical Dosage Forms Tablets, vol. 3, US, Marcel Dekker Inc., 1982, p. 92). Wax can be used by dissolving in an organic solvent such as chloroform/acetone and the like, or suspending in a dispersion medium such as alcohol and the like, or directly applied to the surface of a preparation as a fine powder. However, it is desirable to avoid use of an organic solvent in view of the safety issue caused by a residual solvent, a large scale facility required to prevent accident and environmental pollution, and the like. Moreover, the use of a suspension and a powder may cause non-uniform coating, possibly leading to inconvenience.
Furthermore, polishing with a wax prior to printing may cause easy scratch of prints and stain of the preparation itself as well as containers, which in turn impairs identification function and also reduces the commercial value due to the defective appearance. In addition, some kind of wax provides too much polish that can cause printing failure, and decrease the product yield (e.g., U.S. Pat. No. 4,456,629 (column 1, lines 34-39)).